The invention relates generally to semiconductor manufacturing equipment and, more particularly, to wafer transfer machines.
Generally, semiconductor devices are mass produced by forming many identical circuit patterns on a single silicon wafer which is thereafter cut into many identical dies or xe2x80x9cchips.xe2x80x9d Semiconductor devices, also commonly referred to as integrated circuits, are typically constructed by successively depositing or xe2x80x9cstackingxe2x80x9d layers of various materials on the wafer. Each layer is patterned as necessary to form the desired circuit components. To ensure reliable and predictable operation of integrated circuits, the wafer and deposited materials must be free from contamination. Hence, many fabrication processes must be performed in an environment that is essentially free from contamination. For example, the contamination level requirement for Class 1 cleanliness in semiconductor wafer processing areas or xe2x80x9cclean roomsxe2x80x9d is less than one part (contaminates) per cubic foot. To achieve this high degree of cleanliness, special high volume ventilation systems are used to continuously filter the air. These systems represent a significant contribution to the overall cost of manufacturing semiconductor devices. Accordingly, substantial cost savings can be realized by minimizing the size of the clean rooms and by making the most efficient use of all available clean room space.
A number of different size wafers, ranging from 3 inches in diameter to 8 inches in diameter, are currently produced in the semiconductor industry. In addition, development efforts are underway to produce 10 and 12 inch diameter wafers. While it is economically desirable to have the capability to produce wafers of all sizes, each size wafer generally requires its own special processing equipment. The redundancy in equipment to process different size wafers increases equipment costs as well as the size of the clean room and the associated construction and maintenance costs. Cost and space savings could be realized if some of the same equipment could be used to process different size wafers.
During the manufacture of semiconductor devices, the wafers are subjected to a number of different processes and environmental conditions. Wafer carriers, sometimes also called cassettes or xe2x80x9cboats,xe2x80x9d are used to house the wafers for processing, bulk storing and transporting through the manufacturing processes. One type of wafer carrier is not typically suitable for exposure to all of the different environmental conditions encountered during processing. As a result, the wafers have to be transferred between different types of boats at various times during the production of the semiconductor devices. Wafer transfer machines are used to perform this task. Conventional wafer transfer machines are capable of transferring only one size wafer to and from only one size wafer carrier. It would be advantageous in reducing manufacturing costs to process smaller diameter wafers in larger diameter wafer processing machines. For example, it is desirable to process six inch wafers using eight inch processing machines. Thus, there is a need for a wafer transfer machine that is capable of transferring six inch diameter wafers to and from eight inch diameter wafer carriers to facilitate processing the six inch wafers in eight inch machines. One problem associated with such a transfer, however, is the disparate wafer to wafer spacing in six inch and eight inch wafer carriers. That is, the wafer to wafer spacing is {fraction (3/16)} inch in six inch wafer carriers and xc2xc inch in eight inch wafer carriers. What is needed is a wafer transfer machine that can adjust the wafer to wafer spacing to accommodate the use of both six inch and eight inch wafer carriers.
Accordingly, it is one object of the invention to facilitate the utilization of eight inch wafer processing machines to process six inch wafers. It is another object to reduce the number of machines necessary to support the processing of different size wafers, particularly in a clean room environment. It is a further object of the invention to reduce the equipment and associated clean room costs for the manufacture of semiconductor devices. It is yet another object of the invention to transfer smaller diameter wafers, typically six inch wafers, to and from a larger diameter wafer carrier, typically an eight inch wafer carrier.
These and other objects and advantages may be achieved by a novel apparatus for adjusting the spacing between a series of semiconductor wafers or other such planar objects aligned parallel to one another. The apparatus includes a pair of flat plates disposed parallel to and opposite one another. The plates are spaced apart a distance sufficient to allow the horizontal passage of the objects therebetween. A plurality of elongated opposing dividers are slidably mounted on the plates. The dividers are disposed vertically adjacent to one another at spaced apart intervals and they extend horizontally to support the objects along a portion of their perimeter. A positioning mechanism is operatively coupled to the dividers for changing the spacing between the dividers. The positioning mechanism is operative between a first position wherein the dividers are vertically spaced apart a first distance and a second position wherein the dividers are vertically spaced apart a second distance greater than the first distance. Thus, the spacing between the objects may be changed by moving the positioning mechanism alternately between the first and second positions.
In one preferred version of this spacing adapter apparatus, the positioning mechanism comprises a series of vertically oriented slots in the plates. Each divider is slidably mounted in a respective one of the slots. The first slot has a length L1 and each succeeding slot has a length Ln computed according to the equation Ln=Lnxe2x88x921+xcex94D, where Lnxe2x88x921 is the length of the immediately preceding slot and xcex94D is the difference between the first distance and the second distance. The spacing between the objects is changed in this version of the invention by moving the dividers up and down in the slots.
Another aspect of the invention provides an adjustable wafer transfer machine that allows wafers to be transferred between smaller and larger wafer carriers. The adjustable wafer transfer machine of the present invention includes (1) an adjusting mechanism for changing the spacing between adjacent wafers to accommodate placement of the wafers in either a smaller wafer carrier or a larger wafer carrier, and (2) a transfer mechanism for transferring the wafers between the smaller wafer carrier and the adjusting mechanism and for transferring the wafers between the larger wafer carrier and the adjusting mechanism. In one preferred version of this aspect of the invention, the adjusting mechanism constitutes the spacing adapter apparatus described above. In another preferred version of this aspect of the invention, the transfer mechanism includes a turntable assembly and two transfer arms. The turntable assembly consists of a turntable rotatably mounted on a base. The turntable has a first portion and a second portion. The first portion has an upper surface for receiving the wafer carriers. The adjusting mechanism, such as the preferred spacing adapter, is operatively coupled to the second portion of the turntable. The first transfer arm is positioned adjacent to one end of the turntable and the second transfer arm is positioned adjacent to the other end of the turntable. The turntable is operable to rotate between a first position and a second position. When the turntable is in the first position, the first portion of the turntable (which receives the wafer carriers) is adjacent to the first transfer arm and the second portion of the turntable (on which the adjusting mechanism is mounted) is positioned adjacent to the second transfer arm. When the turntable is in the second position, the first portion of the turntable is adjacent to the second transfer arm and the second portion of the turntable is adjacent to the first transfer arm.